Field of the Invention
The invention pertains to matte substrates comprising water based coating compositions and base substrates. The water based coating composition comprises only small amounts of mineral fillers, refractory fillers and/or organic fillers and may comprise no mineral fillers, refractory fillers or organic fillers. Other matting agents are not used in the invention.
The Related Art
Matte finish, i.e. a dull, no gloss finish having a lack of any or significant luster, is generally achieved by applying a coating material to a substrate. Many different types of substrates can be coated with a material to develop matte finish. One application for such coated substrates is paper stock for books, folders, magazine covers, and coated paper board for containers. Another example is paper that is coated to create matte finish photo paper and printer paper. Matte finishes are also used is in the area of labels, such as package labels.
Matte finish coatings are typically based on polymer resins as the binder and require the use of mineral, refractory and/or organic fillers, or other fillers as agents to lower the gloss. In the prior art, more than 1.0% mineral, refractory or organic fillers, and possibly other fillers, are needed to obtain a matte finish. Matte substrates made with mineral, refractory, organic or other fillers, such as those having more than 1.0% mineral, refractory or organic fillers, and/or other fillers, have disadvantages. These disadvantages include burnish and relatively poor scratch and rub resistance. Burnish resistance and scratch and rub resistance tends to decrease as the gloss of the coated substrate decreases. Moreover, the scratches and burnish marks do not heal such that once the matte substrate is burnished or scratched the wounds are permanent which is particularly disadvantageous when the matte substrate is used for book, folder, and magazine covers or in labeling applications. Further, the coatings in the art are typically high density and, after application to the substrate, cause curl in the coated matte substrate or film which is disadvantageous. Also, films or substrates coated with the conventional materials do not have the desired soft touch feel.
Liquid mineral filled coatings have low solids content and typically at least 12 wet pounds of coating per 3,000 square feet of substrate needs to be applied to achieve a 60° gloss less than 20. Coating at these loadings takes a lot of energy to dry off the volatile material and, also, it takes a lot of heat to laminate these films to another substrate due to heat capacity and heat sink effect of the high loading of mineral fillers.
Further disadvantages include negative effects on processing equipment. For example, conventional films comprising mineral filled matte coatings, such as coatings comprising more than 1.0% mineral, refractory or organic fillers, and/or other fillers, dull the knives that are used to slit the master rolls of coated film down to the correct size. Further, in laminated applications the films comprising conventional material dull the knives used to cut off the films during the lamination step.
In certain applications, use of ultraviolet (“UV”) curable topcoats to the matte substrates is desirable. Such top coating materials do not have excellent adhesion to the conventional mineral filled low gloss coatings, including coatings comprising mineral, refractory, organic or other fillers, including coatings comprising more than 1.0% of such fillers.
Coatings made according to the prior art applied various polymeric binders such as acrylic, polyester, nitrocellulose, melamine, polyurethane and others. The low gloss is achieved by the addition of mineral, refractory or organic fillers and/or other matting agents such as nylon, polyurethane, acrylic, methacrylate, wax based powders, carbodiimide, and the like. Coated low gloss substrates available in the art include a coated low gloss polyamide film, EMBLEM™ 1200M, from Honeywell, Morris Township, N.J., U.S.A., low gloss co-extruded films, films that are produced by chemical laser or mechanical etching, and films that are made low gloss by having a rough pattern embossed in them by heat and/or pressure.
The coating formulations and processes described herein and the matte substrates of the invention comprising such formulations do not have the disadvantages of compositions and substrates in the art. The water based coating composition comprising a water base, such as a polyurethane dispersion, an acrylic dispersion and combinations or reaction products thereof, with a cross-linking agent and optional binder can be applied to a base substrate to create a matte substrate without the use of any or significant matting agents. For example, the compositions may comprise up to about 1.0% mineral filler, refractory filler and/or organic filler or no mineral, refractory or organic fillers, and no other matting agent and achieve a matte finish without the drawbacks associated with compositions in the art.
All parts and percentages set forth in this specification and the claims are on a weight-by-weight basis (wet) unless noted otherwise.